WO2018070144A1

WO2018070144A1 - Rebar corrosion promotion test method and test device using same

Info

Publication number: WO2018070144A1
Application number: PCT/JP2017/032142
Authority: WO
Inventors: 康太郎土井; 廣本　祥子; 英二秋山; 英樹片山; 土谷　浩一
Original assignee: 国立研究開発法人物質・材料研究機構
Priority date: 2016-10-13
Filing date: 2017-09-06
Publication date: 2018-04-19
Also published as: JP6744629B2; JP2018063176A

Abstract

The purpose of the present invention is to provide a novel rebar corrosion promotion test device that can produce iron rust with a composition which is the same as that of iron rust produced in a real environment as simply and in as short a time as possible without altering the properties of concrete. This rebar corrosion promotion test device is characterized in that: the rebar corrosion promotion test device is provided with a pressurization chamber used for increasing oxygen supply quantity and an oxygen supply device or oxygen pressurization device for increasing oxygen pressure inside the pressurization chamber; a cement paste test body, a mortar test body, or a concrete test body is placed in the pressurization chamber; and the oxygen supply quantity to the interior of the cement paste test body, the mortar test body, or the concrete test body is increased by raising the oxygen pressure in the pressurization chamber.

Description

Rebar corrosion acceleration test method and test apparatus used therefor

The present invention relates to a reinforcing bar corrosion acceleration test method for accelerating the reinforcing bar corrosion inside cement paste, mortar, or concrete, and a test apparatus used therefor.

Concrete is indispensable for the material of large structures that require high load capacity such as highways and railway viaducts. Japan entered a period of high economic growth from the 1950s to the 1970s, and a number of concrete structures were built, especially because of the enhancement of infrastructure facilities during the 1964 Tokyo Olympics. About 50 years have passed since then, and many of these structures require repair and rebuilding due to aging. Reinforcing bars are embedded inside the concrete to improve the tensile strength. Accidents such as delamination and collapse of concrete due to aging of concrete structures are often reported. Most of the causes are due to corrosion of reinforcing bars and generated iron rust. In other words, it can be said that it is essential to examine the corrosion behavior inside concrete for the repair and construction of safe and secure structures. For example, Non-Patent Document 1 describes such a reinforcement corrosion diagnosis technique for concrete structures.

Corrosion behavior is examined by placing an iron sample in a corrosive environment. For example, Patent Document 1 proposes a stainless steel corrosion test method suitable for offshore structures such as nuclear reactors, chemical plants, and subsea oil fields. Patent Document 2 proposes a real environment simulated atmospheric corrosion test apparatus. Furthermore, Patent Document 3 proposes a corrosion test method for a wire harness arranged in a living space of an automobile.
On the other hand, since the concrete interior is an alkaline environment and iron is covered with a highly protective oxide film (passive film), corrosion is extremely gradual. For this reason, it is said that it takes several decades or more for the progress of corrosion to such an extent that concrete peels in an actual environment. Deterioration of concrete using newly developed corrosion-resistant steel, weather-resistant steel, and repair agents takes a longer period of time, and it is almost impossible to predict the corrosion of reinforcing steel inside concrete without cracks and other defects in the actual environment It is. Therefore, an accelerated corrosion test that accelerates corrosion of reinforcing bars and can generate iron rust in a short time is essential.

At present, as shown in Non-Patent Document 2, for example, accelerated test methods such as an electrolytic corrosion test method, a wet and dry repeated test method, and an autoclave method have been proposed in order to corrode an iron sample inside a concrete specimen in a short period of time. For introduction of chloride ions, which are considered to be a main factor of corrosion, electrophoresis, salt (NaCl) kneading and the like are performed. In any of the test methods, it is possible to corrode an iron sample in a relatively short time by exposing the specimen to a severe corrosive environment. However, each test method has a problem.

For example, the electrolytic corrosion test method is used to obtain a rebar corrosion weight loss that causes cracks in a short time. The generation of the desired thickness of rust (= corrosion amount) can be achieved in a short time by constant current anodic polarization. However, there are cases where iron rust (iron oxide or iron hydroxide containing chloride ions) that is rarely generated in a real environment is generated. Since iron rust containing chlorides has a very different expansion rate from actual iron rust, it can be said that the exact relationship between the amount of rust and the occurrence of cracks in concrete has not been examined in the electrolytic corrosion test.
In the dry / wet repeat test method, an iron sample is corroded by simulating an actual dry environment and wet environment, and alternately repeating wet and dry. Although this method can generate a rust similar to an iron rust in a real environment, it takes a lot of time and labor compared to other accelerated test methods.

In the autoclave method, corrosion is accelerated by exposing the specimen to a high temperature and high pressure, but the concrete structure may change. For this reason, the concrete strength evaluation cannot be performed accurately.
Electrophoresis and salt kneading are performed in order to introduce chloride ions into the concrete that destroy the passive film on the surface of the iron sample. However, since electrophoresis continues to supply chloride ions, it contains chloride ions. Often iron rust can be produced. In addition, salt kneading may change the mechanical properties of the concrete specimen.
In view of the above, there is a need for a new corrosion acceleration test method that can generate iron rust having the same composition as iron rust generated in an actual environment without changing the properties of the concrete as easily and as quickly as possible.

WO03 / 073073 A2 JP 2006-258506 A WO2010 / 016265 A1

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems, and a new method for promoting corrosion of reinforcing steel bars, which can generate iron rust having the same composition as iron rust generated in an actual environment without changing the properties of concrete, as easily and as quickly as possible. The purpose is to provide.

The reinforcing bar corrosion promotion test apparatus of the present invention includes a pressurization chamber used for increasing the oxygen supply amount, and an oxygen supply device or an oxygen pressurization device for increasing the oxygen pressure in the pressurization chamber, and the pressurization chamber A cement paste test specimen, a mortar test specimen, or a concrete test specimen is installed in the inside, and the oxygen pressure in the pressurized chamber is increased to enter the cement paste test specimen, the mortar test specimen, or the concrete test specimen. The oxygen supply amount is increased.

In the reinforcing bar corrosion acceleration test apparatus of the present invention, it is preferable to have an aqueous NaCl solution accumulated in the pressurized chamber and immerse the cement paste specimen, mortar specimen, or concrete specimen in the NaCl aqueous solution.
In the reinforcing bar corrosion acceleration test apparatus of the present invention, preferably, the NaCl aqueous solution filled in the pressurized chamber is 8.2 × 10 ⁻⁵ kg / m ³ or more and 50 kg / m ³ or less in terms of concrete per unit volume. The chloride ion concentration may be as follows. 8.2 × 10 ⁻⁵ kg / m ³ (0.02 mmol / L) is a representative value of the chloride ion concentration of rainwater, and is a practical lower limit for concrete structures used inland. Chloride ion concentration exceeding 50 kg / m ³ is not possible in marine concrete when sea sand is used as coarse aggregate or when the upper limit of saturated NaCl solution is exceeded when NaCl powder is directly mixed into concrete. This is a practical upper limit. In addition, when the saturated NaCl solution is kneaded into marine concrete at a water cement ratio of 50%, for example, it is about 39.3 kg / m ³ in terms of concrete (Japan Society of Civil Engineers “Concrete Standard Specification <Construction> Chapter 20 Marine Concrete” (See formula for More preferably, the NaCl aqueous solution filled in the pressurized chamber may have a chloride ion concentration of 2 kg / m ³ or more and 10 kg / m ³ or less in terms of concrete per unit volume, particularly preferably seawater chlorination. It is good that it is 5 kg / m ³ corresponding to the physical ion concentration.
In the reinforcing bar corrosion acceleration test apparatus of the present invention, preferably, the concentration of the NaCl aqueous solution is adjusted to be the same as the NaCl concentration of water used for mixing the mortar or cement paste.

In the reinforcing bar corrosion acceleration test apparatus of the present invention, preferably, further comprising a humidity control unit for controlling the humidity in the pressurization chamber, and an oxygen pressure control unit for increasing the oxygen pressure in the pressurization chamber, The oxygen pressure control unit may increase the amount of oxygen supplied into the cement paste specimen, mortar specimen, or concrete specimen.
In the reinforcing bar corrosion acceleration test apparatus according to the present invention, preferably, the humidity control unit humidifies a gas supplied by a humidifier and / or installs a saturated solution of a predetermined inorganic salt in a chamber, and pressurizes. It is good to control the humidity in the chamber.
In the reinforcing bar corrosion acceleration test apparatus of the present invention, preferably, the increase in oxygen pressure in the pressurization chamber is 2 to 200 times based on the oxygen partial pressure in the atmosphere. If it is less than 2 times, the increase in the amount of oxygen supplied into the cement paste specimen, mortar specimen, or concrete specimen is not sufficient, and the reinforcement of reinforcing steel bars is not sufficient. When it exceeds 200 times, excessive pressure resistance is required for the pressure chamber, and the equipment price increases. More preferably, the increase in the oxygen pressure in the pressurizing chamber is 15 times or more and 100 times or less based on the oxygen partial pressure in the atmosphere.

Reinforcing bar corrosion acceleration test method of the present invention, a cement paste test body, a mortar test body, or a concrete test body is installed in a pressure chamber, the oxygen pressure in the pressure chamber is increased, the cement paste test body, This is a test method that increases the amount of oxygen supplied into the mortar test specimen or concrete test specimen and promotes corrosion of reinforcing bars embedded in the cement paste test specimen, mortar test specimen, or concrete test specimen.
In the reinforcing bar corrosion acceleration test method of the present invention, it is preferable to further include a step of adjusting the humidity in the pressure chamber by installing a saturated solution of a predetermined inorganic salt in the pressure chamber.

In the reinforcing bar corrosion acceleration test method of the present invention, a NaCl aqueous solution that adjusts to a predetermined chloride ion concentration in terms of concrete as a specimen is prepared, and the NaCl aqueous solution is filled in a pressurized chamber. A cement paste specimen, a mortar specimen, or a concrete specimen is immersed in an aqueous NaCl solution, and the oxygen pressure in the pressurized chamber is increased to enter the cement paste specimen, the mortar specimen, or the concrete specimen. This is a test method for increasing the amount of oxygen supplied to promote corrosion of reinforcing bars embedded in the cement paste specimen, mortar specimen, or concrete specimen.

According to the present invention, by increasing the amount of oxygen supplied into the concrete, mortar and cement paste specimens, the corrosion reaction of the iron sample embedded in the specimen can be promoted. More specifically, by promoting the oxygen reduction reaction, which is the cathodic reaction of the corrosion reaction, by increasing the oxygen supply amount, it is possible to promote the iron oxidation reaction, which is the anodic reaction that proceeds in a pair with the cathodic reaction.

FIG. 1A is a schematic view of a cement paste specimen or a mortar specimen according to one embodiment of the present invention. FIG. 1B is an external appearance photograph of a cement paste specimen or a mortar specimen according to one embodiment of the present invention. FIG. 2 is a conceptual configuration diagram of a pressurized chamber according to an embodiment of the present invention. FIG. 3A is a diagram showing the relationship between the oxygen diffusion limit current density and the reciprocal of fog obtained from the cathode polarization curves of various fog cement pastes or iron samples inside mortar. FIG. 3B is a graph showing the relationship between the oxygen diffusion limit current density and the reciprocal of the fog obtained from the cathode polarization curves of various fog cement pastes or iron samples inside the mortar, and a part of the fog range of FIG. 3A. FIG. FIG. 4A is a view showing an optical microscope image of the surface of an iron sample when the corrosion acceleration test is performed in an aqueous NaCl solution embedded in a cement paste. FIG. 4B is a diagram showing an optical microscope image of the surface of the iron sample when the corrosion acceleration test is performed in an aqueous NaCl solution embedded in mortar. FIG. 4C is a diagram showing an optical microscope image of the surface of the iron sample when the corrosion acceleration test is performed in a NaCl aqueous solution under 0.5 MPa pressurized oxygen embedded in cement paste. FIG. 4D is a diagram showing an optical microscope image of the surface of the iron sample when the corrosion acceleration test is performed in a NaCl aqueous solution under a 0.5 MPa pressurized oxygen, embedded in mortar. FIG. 5A is a diagram showing a cross-sectional SEM reflected electron image of an iron sample when the corrosion acceleration test was performed in an aqueous NaCl solution embedded in cement paste. FIG. 5B is a diagram showing a cross-sectional SEM backscattered electron image of an iron sample when the corrosion acceleration test was conducted in an aqueous NaCl solution embedded in mortar. FIG. 5C is a diagram showing a cross-sectional SEM backscattered electron image of an iron sample when the corrosion acceleration test is performed in a NaCl aqueous solution under 0.5 MPa pressurized oxygen embedded in cement paste. FIG. 5D is a diagram showing a cross-sectional SEM backscattered electron image of the iron sample when the corrosion acceleration test was conducted in a NaCl aqueous solution under 0.5 MPa pressurized oxygen embedded in mortar. FIG. 5E is a diagram showing an elemental distribution of iron by EDS measurement of a cross section of an iron sample when the corrosion acceleration test is performed in a NaCl aqueous solution under 0.5 MPa pressurized oxygen embedded in mortar. FIG. 5F is a diagram showing an oxygen element distribution by EDS measurement of a cross section of an iron sample when a corrosion acceleration test is performed in a NaCl aqueous solution under 0.5 MPa pressurized oxygen embedded in a mortar. FIG. 6 is a Raman spectrum of a corrosion product on the surface of an iron sample when buried in a mortar and subjected to a corrosion acceleration test under a pressurized oxygen of 0.5 MPa.

Hereinafter, the present invention will be described with reference to the drawings.
1A and 1B are explanatory diagrams of a cement paste test body or a mortar test body according to an embodiment of the present invention, FIG. 1A is a schematic view, and FIG. 1B is an appearance photograph.
In the figure, a cement paste test body or mortar test body 10 is composed of a cement paste or mortar 11 made of, for example, a cylindrical body having an outer diameter D of 30 mm and a height H of 25 mm, and an iron sample 12 accommodated therein. ing. Here, the cement paste is a solidified cement paste obtained by mixing a cement material with water. Mortar is a mixture of cement paste with sand (fine aggregate). In the case of Portland cement, the cement material is limestone, clay, silica, iron oxide raw material, and gypsum. These raw materials are prepared, pulverized in a raw material mill, and baked in a rotary kiln at a high temperature of 1450 ° C. or higher to form a clinker that is a collection of hydraulic compounds. The clinker is pulverized to produce Portland cement. Examples of the cement material include blast furnace cement, fly ash cement, silica cement, ultrafast cement, and alumina cement in addition to Portland cement. Instead of the cement paste specimen or the mortar specimen 10, a concrete specimen may be used. Concrete means cement paste mixed with sand (fine aggregate), gravel (coarse aggregate), and other admixtures as required. Admixture materials include AE materials that entrain closed cells, water-reducing materials that disperse cement, curing accelerators, rust inhibitors, adhesion mortar stabilizers, setting retarders, accelerators, quick setting agents, shrinkage reducing agents, and separation reduction. Agents, foaming agents, foaming agents, anti-freezing agents, cold resistance promoting agents and the like.

In the iron sample 12, the bottom surface of the iron sample 12 is in contact with the cement paste or the mortar 11, and the surface and the peripheral side surface of the iron sample 12 are covered with a coating layer 15 of epoxy resin. A conductive wire 14 is fixed to the surface of the iron sample 12 in contact with an insulating rod 13 made of vinyl chloride or the like. The cement paste or fog 16 of the mortar 11 on the bottom surface of the iron sample 12 is appropriately selected within a range of 1 to 50 mm. The conductive wire 14 is made of a conductive metal wire, such as a copper wire.

FIG. 2 is a conceptual configuration diagram of a pressurized chamber according to an embodiment of the present invention.
In the figure, a reinforcing bar corrosion acceleration test apparatus 20 as a pressurized chamber includes a casing 21, a flange 22, a lid 23, an observation window 24, an oxygen supply valve 25, an oxygen release valve 26, a pressure gauge 27, a NaCl aqueous solution 28, and A test body support plate 29 is provided.

The housing 21 has a specification as a pressure vessel of 2 MPa or more, preferably 5 MPa or more. Since the atmospheric pressure is about 0.1 MPa, the pressure vessel material is preferably made of steel or titanium. Titanium is more resistant to local corrosion due to salt than steel. A flange 22 is provided at the top opening of the housing 21, and the sealed state inside the housing 21 is maintained by a lid portion 23 and a sealing material (not shown). The observation window 24 is provided on the lid portion 23 and is made of transparent glass or the like in order to visually observe the state inside the housing 21. The oxygen supply valve 25 is a valve for supplying oxygen into the housing 21 and is configured as an oxygen supply device or an oxygen pressurization device, and is connected to, for example, an oxygen cylinder. The oxygen release valve 26 is a valve for releasing oxygen from the inside of the housing 21 and is connected to, for example, a piping system for oxygen circulation. The pressure gauge 27 is a pressure gauge for measuring the oxygen pressure inside the housing 21. The reinforcing bar corrosion acceleration test apparatus 20 may further include an oxygen pressure control unit that controls the pressure of oxygen using the pressure gauge as described above as a meter.

The NaCl aqueous solution 28 is stored in the housing 21 and may be in a state in which the cement paste test body or mortar test body 10 is immersed, or in a state where the cement paste test body or mortar test body 10 is exposed. The test body support plate 29 is a plate material that supports the cement paste test body or the mortar test body 10 provided in the housing 21.
The reinforcing bar corrosion acceleration test apparatus 20 may further include a humidity control unit that controls the humidity in the pressurized chamber.
The range of the humidity in the pressurized chamber is preferably 30% relative humidity (based on a saturated aqueous solution of MgCl ₂ ) or more and 98% (based on a saturated aqueous solution of K ₂ SO ₄ ). This humidity range is appropriate as an experimental condition because it corresponds to changes in wet and dry conditions when concrete is usually placed outdoors.

Next, each component of the cement paste specimen or mortar specimen 10 in the examples will be described in more detail.
The iron sample 12 was a 99.5% iron plate (Niraco Co., Ltd.) with a material / shape having a thickness of 1 mm. The iron plate was cut to a sample area of 5 × 5 mm ² , polished to # 800 with SiC water-resistant abrasive paper (Marumoto Struers Co., Ltd.), and ultrasonically washed with ethanol for 5 minutes. Thereafter, a conductive wire was soldered to the back surface, and the other surfaces were insulated with an epoxy resin (Shobond Construction Co., Ltd.).

Subsequently, the iron sample 12 produced above was embedded in a cement paste or mortar to obtain a cement paste specimen or mortar specimen 10. As shown in FIG. 1A, in the cement paste specimen or mortar specimen 10, the fog 16 was changed to 1 to 50 mm. However, for a test piece with a cover of 20 mm or more, the test piece was enlarged so that the distance from the side surface or top surface to the iron sample surface was not smaller than the cover. NaCl is not kneaded into the specimen used for the potentiodynamic cathode polarization test, and [Cl ⁻ ] = 5 kg / m ³ (in terms of concrete) is applied to the specimen subjected to the accelerated corrosion test by increasing oxygen supply. A 0.33M NaCl aqueous solution was kneaded. When placing cement paste or mortar, standard cement for mechanical testing and standard sand provided by the Cement Association were used, and the water cement ratio was 60% and the cement fine aggregate ratio was 1: 3. Each curing period was 28 days and was cured in water.

Table 1 shows the composition of cement paste and mortar used in each test and the chloride ion concentration of kneaded NaCl.

Subsequently, the measurement of the potentiodynamic cathode polarization curve will be described.
In order to examine the oxygen reduction reaction on the surface of an iron sample embedded in a cement paste specimen or a mortar specimen, a dynamic potential cathodic polarization curve was measured. A Hg / HgO electrode was used as a reference electrode (−0.098 V vs. SHE (1M NaOH)), and a platinum wire was used as a counter electrode. The potential sweep rate was 20 mV / min, and the polarization was measured from the natural potential to -1 V (vs. Hg / HgO). The solution was saturated Ca (OH) ₂ at room temperature. After curing the test body, it was immersed in the solution for 10 minutes, and polarization was started after confirming that the natural potential became steady. The fog of the test specimen was 1, 2, 5, 10, 20, 50 mm for the cement paste specimen, and 3, 5, 10, 20, 50 mm for the mortar specimen. As a comparison, a sample (covering 0 mm) that was not embedded in cement paste or mortar was prepared, and cathodic polarization measurement was performed in the same manner.

Next, the corrosion acceleration test by oxygen pressurization will be described.
Corrosion of reinforcing steel inside the concrete is remarkably suppressed compared to that in an alkaline aqueous solution because the oxygen diffusion inside the concrete is very slow. Inspired by the accelerated corrosion test.

In this pressurized chamber, a cement paste specimen or a mortar specimen immersed in a NaCl aqueous solution adjusted so that [Cl ⁻ ] = 5 kg / m ^{3 in} terms of concrete per unit volume is installed, and oxygen in the chamber The oxygen supply in the atmosphere was increased by increasing the pressure. The oxygen pressure in the chamber was 0.5 MPa (5 atm), and the oxygen supply amount into the cement paste or mortar was increased under an oxygen supply pressure 25 times the atmospheric pressure. The test period was 30 days. For comparison, a cement paste or a mortar specimen prepared in the same manner was immersed in an aqueous NaCl solution of [Cl ⁻ ] = 5 kg / m ³ (concrete conversion, 1.03 mol / L) in the air for 30 days. The fog of the used cement paste specimen or mortar specimen was 5 mm.

After the accelerated corrosion test, the cement paste specimen or mortar specimen is split and an iron sample is taken out. The surface of the iron specimen is observed using an optical microscope (3D1shot, Keyence), and the specimen is observed using a scanning electron microscope (Quanta FEG, FEI). Cross-sectional observation was performed. Furthermore, in order to analyze the crystal structure of the iron rust generated on the iron sample surface, laser Raman spectroscopy measurement of the iron sample surface after the test was performed. (RAMAN plus, nanophoton) was used for laser Raman spectroscopy. The laser wavelength is 532 cm ⁻¹ . When time was required from the removal of the iron sample to the analysis, the iron sample was stored in a vacuum desiccator with silica gel.

Subsequently, the oxygen reduction reaction on the iron surface inside the cement paste or mortar will be described. The iron sample embedded in the cement paste significantly reduced the oxygen reduction current density in the vicinity of the natural potential in any fog (1 mm to 50 mm) compared to the sample exposed to the solution (0 mm fog). Also, the oxygen reduction current density near the natural potential tended to decrease as the fogging increased.

Also in the inside of the mortar, the oxygen reduction current density near the natural potential was remarkably reduced as compared with the cover of 0 mm, and the value decreased as the cover increased. When the inside of the cement paste or the inside of the mortar was compared, there was a tendency that the oxygen reduction current density inside the cement paste decreased with the same cover. Dissolved oxygen is supplied to the water layer in the pores of the cement paste and mortar by diffusion. It is considered that the oxygen reduction current density of the cathode polarization curve decreased because the distance between the outside and the iron surface, that is, the fogging, increased the time required for oxygen diffusion. It is known that there are larger pores in the mortar inside the cement-fine aggregate interface than in the cement paste, and it has been reported that the larger the pores, the larger the oxygen diffusion coefficient. . From these results, it is considered that the oxygen reduction current density increased because water existing in relatively large pores inside the mortar became a path for oxygen diffusion.

Assuming that the oxygen reduction reaction inside the cement paste or mortar is limited by oxygen diffusion, the oxygen reduction current density in cathodic polarization is expressed as the oxygen diffusion current density. That is, it can be applied to a diffusion equation consisting of the oxygen diffusion current density and the diffusion layer thickness. The oxygen diffusion equation is expressed by the following equation.

Where i _L is the oxygen diffusion limit current density (A / m ² ), z is the valence number, F is the Faraday constant (C / mol), D is the dissolved oxygen diffusion constant (m ² / s), and C is the dissolved oxygen. Offshore concentration (mol / m ³ ), δ is the thickness (m) of the diffusion layer. Here, it was assumed that all the fog was a diffusion layer.
FIG. 3A and FIG. 3B are diagrams showing the relationship between the oxygen diffusion limit current density and the reciprocal of the fog obtained from the cathodic polarization curves of iron samples inside various cement pastes. FIG. 3A shows a range of 1 mm to 50 mm of fog, and FIG. 3B shows an enlarged range of 10 mm to 50 mm of the cover of FIG. 3A. In addition, since the steady state of the electric current was not recognized by the cathode polarization inside cement paste or mortar, the current density at a potential lower by 50 mV than the natural potential was adopted as the oxygen diffusion limit current density.

From FIG. 3A, a linear proportional relationship was recognized between the oxygen diffusion limit current density and the reciprocal of the fog in the range from 1 mm to 10 mm. Therefore, in this range, the cement paste or the inside of the mortar can be regarded as a macroscopically uniform diffusion layer.
From FIG. 3B, in the range of 20 mm to 50 mm, the critical diffusion current density and the reciprocal of the fog deviate from the linear relationship. From these results, it is shown that the thickness of the oxygen diffusion layer inside the cover is 10 mm or more and less than 20 mm. If the cover is 10 mm or less, the corrosion of the reinforcing bars is the rate of oxygen reduction, and oxygen on the iron surface It has been shown that increasing the supply can promote iron corrosion.

Next, accelerated generation of iron rust inside cement paste or mortar under oxygen pressure will be described.
4A to 4D show optical microscope images of the surface of the iron sample when the accelerated corrosion test is performed under each condition. Here, the fogging of the cement paste or the mortar at the time of performing the accelerated corrosion test was performed at 5 mm where it is estimated that the corrosion of iron is within the range of oxygen diffusion rate control. 4A and 4B, almost no corrosion was observed in the samples embedded in cement paste or mortar and tested in an aqueous NaCl solution in the atmosphere. From FIG. 4C, more corrosion products were observed in the sample embedded in the cement paste and tested in an aqueous NaCl solution under 0.5 MPa pressurized oxygen than in the sample tested in the atmosphere. From FIG. 4D, the number of samples embedded in mortar and tested in a NaCl aqueous solution under 0.5 MPa pressurized oxygen was larger than that of samples embedded in the atmosphere and cement paste and tested under pressurized oxygen. The adhesion of corrosion products was observed.

In order to examine the thickness of the iron rust generated by the accelerated corrosion test, a cross-sectional SEM observation of the sample was performed. 5A to 5F show cross-sectional SEM backscattered electron images of iron samples tested under various conditions. From FIG. 5A and FIG. 5B, in the sample embedded in cement paste or mortar and tested in an aqueous NaCl solution in the atmosphere, the presence of corrosion products was not confirmed from the cross-sectional images. From FIG. 5C and FIG. 5D, a corrosion product of several μm was generated in a sample embedded in a cement paste or mortar and tested in a NaCl aqueous solution under 0.5 MPa of pressurized oxygen. However, in the cross-sectional views of FIG. 5C and FIG. 5D, portions where much corrosion was observed in FIG. 4C and FIG. 4D were photographed. The distribution of iron and oxygen by EDS measurement at the same location as in FIG. 5D is shown in FIGS. 5E and 5F. From the result of EDS measurement, it was confirmed that the corrosion product obtained under oxygen pressure was iron oxide, that is, iron rust. Table 2 shows the thickness of each iron rust determined from the cross-sectional SEM image.

Furthermore, the estimated iron rust thickness under each condition obtained from the oxygen-limited diffusion current obtained by cathodic polarization is also shown. Here, the iron rust expansion coefficient was calculated as 2.55. The thickness of the iron rust obtained by SEM observation was 1 μm or less for a sample which was embedded in cement paste or mortar with a cover of 5 mm and tested in the atmosphere, and embedded in the cement paste with a cover of 5 mm and tested under oxygen pressure. The sample was about 1.7 μm, and the sample embedded in mortar with a cover of 5 mm and tested under oxygen pressure was about 3.7 μm. The thickness of each iron rust was taken as the average thickness of the iron oxide measured by taking a 5-point SEM image at random. Both values were close to the expected thickness of iron rust obtained from the oxygen limit diffusion current density. From these results, it was clarified that the amount of oxygen supply has a great influence on the generation of iron rust inside the cement paste or mortar, and that oxygen pressurization is effective in accelerating the generation of iron rust.

Next, the structural analysis of iron rust generated under oxygen pressure will be described.
As described above, the accelerated iron rust is required to have the same composition as the iron rust generated over decades in the actual environment. The structure of iron rust produced under oxygen pressure was investigated using laser Raman spectroscopy. Takatani et al. Reported that the iron rust generated inside the concrete in an alkaline environment is Fe ₃ O ₄ (magnetite) and iron oxohydroxide (α-FeOOH (goethite), γ-FeOOH (lepidocrocite)). Satoshi Takatani, 4 others, “Production process and electrochemical properties of corrosion products of reinforcing bars in concrete”, JSCE Proceedings E2 (Materials / Concrete Structure), 2015, Vol. 71, No. 3, p. 235-247). FIG. 6 shows a Raman spectrum of the corrosion product on the surface of the iron sample embedded in mortar with a cover of 5 mm and tested under pressurized oxygen of 0.5 MPa. As shown in FIG. 6, the corrosion product contains Fe ₃ O ₄ , α-FeOOH, and γ-FeOOH indicated by symbols in the figure, and rust having the same composition as iron rust in the actual environment was generated. confirmed. On the other hand, the iron rust on the sample surface tested in cement paste was too thin to obtain a Raman spectrum.

The oxygen pressurization test method of the present invention can produce iron rust similar to that in the actual environment than the electrolytic corrosion test method, is a simple method in a shorter time than the dry and wet repeated test method, and is more concrete than the autoclave method. Since this test method does not impair the mechanical properties, it is very effective as a new accelerated test method for concrete internal corrosion.

DESCRIPTION OF SYMBOLS 10 Cement paste test body, mortar test body, or concrete test body 11 Cement paste or mortar 12 Iron sample 13 Insulating bar 14 Conductor 15 Cover layer 16 Cover 20 Reinforcing bar corrosion acceleration test apparatus (pressure chamber)
21 Housing 22 Flange 23 Lid 24 Observation window 25 Oxygen supply valve 26 Oxygen release valve 27 Pressure gauge 28 NaCl aqueous solution 29 Specimen support plate

Claims

A pressurized chamber used to increase oxygen supply;
An oxygen supply device or an oxygen pressurization device for increasing the oxygen pressure in the pressurization chamber,
A cement paste specimen, a mortar specimen, or a concrete specimen is installed in the pressurized chamber, and the oxygen pressure in the pressurized chamber is increased to increase the cement paste specimen, mortar specimen, or concrete specimen. Reinforcing bar corrosion promotion test device characterized by increasing the amount of oxygen supplied to the interior of the steel.
Furthermore, it has a NaCl aqueous solution that accumulates in the pressure chamber,
The reinforcing corrosion test apparatus according to claim 1, wherein a cement paste specimen, a mortar specimen, or a concrete specimen is immersed in the NaCl aqueous solution.
3. The reinforcing bar according to claim 2, wherein a chloride ion concentration in the NaCl aqueous solution is 8.2 × 10 −5 kg / m 3 or more and 50 kg / m 3 or less in terms of concrete per unit volume. Corrosion acceleration test equipment.
The density | concentration of the said NaCl aqueous solution is adjusted so that it may become the same as the NaCl density | concentration of the water used for kneading mortar, a cement paste, or concrete. Rebar corrosion acceleration test equipment.
In the reinforcing bar corrosion promotion test apparatus according to any one of claims 1 to 4,
Furthermore, a humidity controller that controls the humidity in the pressurizing chamber;
An oxygen pressure controller that raises the oxygen pressure in the pressurizing chamber;
Reinforcing bar corrosion acceleration test device characterized in that oxygen supply amount to the inside of the cement paste test body, mortar test body, or concrete test body is increased by the oxygen pressure control unit.
The humidity controller controls humidity in the pressurized chamber by humidifying a gas supplied by a humidifier and / or installing a saturated solution of a predetermined inorganic salt in the chamber. Item 6. The reinforcing bar corrosion acceleration test apparatus according to Item 5.
7. The reinforcing bar corrosion acceleration test according to claim 1, wherein the increase in the oxygen pressure in the pressurizing chamber is not less than 2 times and not more than 200 times based on the oxygen partial pressure in the atmosphere. apparatus.
Install a cement paste specimen, mortar specimen, or concrete specimen in the pressure chamber,
Increasing the oxygen pressure in the pressurized chamber to increase the amount of oxygen supplied into the cement paste specimen, mortar specimen, or concrete specimen,
A test method for promoting the corrosion of reinforcing bars embedded in the cement paste specimen, mortar specimen, or concrete specimen.
Further, the reinforcing corrosion test method according to claim 8, wherein a saturated solution of a predetermined inorganic salt is installed in the pressurized chamber to adjust the humidity in the pressurized chamber.
Adjust the NaCl aqueous solution so as to have a predetermined chloride ion concentration in terms of concrete as the specimen,
Fill the pressurized chamber with the NaCl aqueous solution,
Immerse the cement paste specimen, mortar specimen, or concrete specimen in the NaCl aqueous solution in the pressurized chamber,
Increasing the oxygen pressure in the pressurized chamber to increase the amount of oxygen supplied into the cement paste specimen, mortar specimen, or concrete specimen,
A test method for promoting the corrosion of reinforcing bars embedded in the cement paste specimen, mortar specimen, or concrete specimen.